Slow printing on a Durst 138 with a CLS301 head

Good evening and greetings from Australia
I am interested in the enlarging times one might expect using a Durst 138 with a CLS301 head for black and white printing. I have acquired one and am teaching myself quality printing. The machine is lovely to use but it is very slow compared to my LPL6600 condenser. For instance I printed the same negative on both machines - 42 seconds on the LPL using a 0 filter and 620 seconds on the Durst using 50 Y on the dichroic head (75 mm lens on the LPL, 175 mm lens on the Durst, 6x6 negative, 8x10 (inch) print). Ten minutes seems a long time to be leaning against the wall, wondering if the timer is actually working. I should add that print quality was fine and effectively the same (or possibly even better) as the LPL. So my questions are:

1: How long do other people have to expose on a Durst 138 with a CLS head?
2: Am I missing somethings such as a switch that boosts the power up?

I should add that the bulbs (2x150 watt) in the Durst is new. The Mixing box is home made cardboard insert lined with aluminium foil into the 5x4 mixing box. The finish is about as shiny as the Durst-supplied 5x4 box, so I don't that is an issue. I know that lens focal length is a factor, but whatever the focal length of the lens, printing seems slow.

So, do I just have to be patient or is there something I could or should do?

Slow printing on a Durst 138 with a CLS301 head

Hi Leon
Our Durst 138 CLS301 is a 5x7 colour head with two 120 volt 300 watt bulbs and a Durst TRA301 power transformer. The formats we use on this enlarger aare 35mm, medium format 645 up to 6x9, and large format 4x5 and 5x7.
In Canada, we use the 110/120volt plug but the transformer also has the European 220/240 volt plug.
Our enlarger doesn't seem slow, compared to our other enlargers.

At the moment we are using a Rodenstock 150mm lens which has F stops ranging from F5.6 (wide aperture - large hole, lets the most light through the lens) to F45 (narrow aperture - small hole allows less light through the lens). The wider F stop, in our lens 5.6, takes less time to get to black than using F45. Some photographers prefer not to use the widest opening of a lens....but to move 2 or 3 stops down. We mostly use F11 or F16.

Check your lenses to see what F stop you are using on each enlarger lens for comparison.

I'm sure others will chime in to help you as well. Wonderful enlargers, aren't they? Good luck with this.

Leon here. Yes, that's my current theory since they do look quite thick and dense (got no idea however how they should look). I should add that everything else looks fine on it (the bulbs are 2x300 watt, not 2x150 watt as I quoted above). However even when I use the correct mixing box for a 5x4 neg the printing time is still in the order of minutes. Re the lenses, this is using them at the largest stop since if I stop down the printing time becomes too much to bear.

Check and make sure the filters are moving out of the way properly. If your cyan filter is engaged it could be cutting the light down. I don't know if there is a ND filter in that head, but look for any obstructions in the light path. Even a very thick diffusion plate shouldn't cut the light by that many stops.

Durst 138 with a CLS301 head

Hi Leon
I went downstairs and took another look at our Durst.

In the CLS301 head, there is a filter drawer, its just under the colour dials. Is this drawer empty?

We have 3 mixing boxes, Medium format, 4x5 and 5x7. The 4x5 is quite large, 4 5/8" x 5 5/8" and 6 1/2" deep.
The sides of the mixing boxes are made from very shiny aluminum with 1/8" thick white plexiglass in the bottom.
The plexiglass is scored with very fine (faint) circles radiating from the centre of the box.

We did have to replace the light sockets when we first got the enlarger as they were black.

What type of film holder are you using, the glass (one size fits all) holder (which uses blades to mask to the edges of the film, therefore putting maximum light through the film itself) or film holders sized to the shape of the film?

Using a Sekonic Light meter on ambient light setting, ISO 100, with the white globe of the light meter 22" directly below the lens, using a wide open lens, aperture 5.6, the light meter exposure reading shows 8 seconds. This type of reading will tell you the strength of the light.

In the CLS301 head, there is a filter drawer, its just under the colour dials. Is this drawer empty?

We have 3 mixing boxes, Medium format, 4x5 and 5x7. The 4x5 is quite large, 4 5/8" x 5 5/8" and 6 1/2" deep.
The sides of the mixing boxes are made from very shiny aluminum with 1/8" thick white plexiglass in the bottom.
The plexiglass is scored with very fine (faint) circles radiating from the centre of the box.

We did have to replace the light sockets when we first got the enlarger as they were black.

What type of film holder are you using, the glass (one size fits all) holder (which uses blades to mask to the edges of the film, therefore putting maximum light through the film itself) or film holders sized to the shape of the film?

Using a Sekonic Light meter on ambient light setting, ISO 100, with the white globe of the light meter 22" directly below the lens, using a wide open lens, aperture 5.6, the light meter exposure reading shows 8 seconds. This type of reading will tell you the strength of the light.

Thanks for that and I think the answer is in your reply. I had a solid look into the works (as far as I could without disassembling the machine) and it all looks fine, but the bottom diffuser is, I think, not original. You note that yours has concentric circles - I bet it is a fresnel surface built into the diffuser to give the light box a focussing capacity in the same way that a condenser is focussed ( I seem to recall that tlr cameras often had a fresnel under the ground glass to brighten up the image too). I'll get a light meter and compare it with yours, but the use of a fresnel would certainly be logical and would concentrate the light. I'll work on that thesis for the moment.

Problem Solved - Thanks Guys

Originally Posted by leon bren

Thanks for that and I think the answer is in your reply. I had a solid look into the works (as far as I could without disassembling the machine) and it all looks fine, but the bottom diffuser is, I think, not original. You note that yours has concentric circles - I bet it is a fresnel surface built into the diffuser to give the light box a focussing capacity in the same way that a condenser is focussed ( I seem to recall that tlr cameras often had a fresnel under the ground glass to brighten up the image too). I'll get a light meter and compare it with yours, but the use of a fresnel would certainly be logical and would concentrate the light. I'll work on that thesis for the moment.

Leon

I went to the $2 shop and bought a plastic "magnifying sheet" (aka fresnel) and cut it to fit onto the bottom of the light mixing box. That made things better but the diffuser was still losing too much light. I replaced it with tracing paper (remember that?) and the fresnel/$2 magnifying sheet and it gives a uniform light and has increased the speed down to 20-30 seconds at stop 11 for an 8x10 print. I guess that the old diffuser had cracked and been replaced with a heavier and non-focussing one. Still playing around with it for negative sizes other than 4x5 but it has certainly made it useable. I should add that it is a lovely enlarger to use.